<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    /*.parent{*/
    /*    width: 300px;*/
    /*    height: 300px;*/
    /*    background: #63a35c;*/
    /*    position: relative;*/
    /*}*/
    /*.child{*/
    /*    width: 100px;*/
    /*    height: 100px;*/
    /*    background: #9a6e3a;*/
    /*    position: absolute;*/
    /*    top: 0;*/
    /*    right: 0;*/
    /*    bottom: 0;*/
    /*    left: 0;*/
    /*    margin: auto;*/
    /*}*/
.parent{
    width: 300px;
    height: 300px;
    background: #00a4ff;
    display: flex;
    justify-content: center;
    align-items: center;
}
.child{
    width: 100px;
    height: 100px;
    background: #17deb9;
}


</style>
<body>
<div class="parent">
    <div class="child"></div>
</div>
</body>
</html>

